Application of unmodified mouse monoclonal antibodies in the treatment of human diseases may be problematic for several reasons. First, an immune response against the mouse antibodies may be mounted in the human body. Second, the mouse antibodies may have a reduced half-life in the human circulatory system. Third, the mouse antibody effector domains may not efficiently trigger the human immune system.
Several reports relate to eliminating the foregoing problems. For example, Junghans et al., Cancer Res., 50:1495-1502 (1990), describe the utilization of genetic engineering techniques to link DNA encoding murine variable domains to DNA encoding human constant domains, creating constructs which, when expressed, generate a hybrid mouse/human chimeric antibody.
Also by genetic engineering techniques, the genetic information from murine hypervariable complementarity determining regions (hereinafter referred to as "CDRs") may be inserted in place of the DNA encoding the CDRs of a human monoclonal antibody to generate a construct encoding a human antibody with murine CDRs. This technique is known as "CDR grafting". See, e.g., Jones et al., Nature, 321, 522-525 (1986); Junghans et al., supra.
Protein structure analysis may be used to "add back" murine residues, again by genetic engineering, to first generation variable domains generated by CDR grafting in order to restore lost antigen binding capability. Queen et al., Proc. Natl. Acad. Sci. USA, 86, 10029-10033 (1989); Co, et al., Proc. Natl. Acad. Sci. USA, 88, 2869-2873 (1991) describe versions of this method. The foregoing methods represent techniques to "humanize" mouse monoclonal antibodies.
As a result of the humanization of mouse monoclonal antibodies, specific binding activity of the resulting humanized antibodies may be diminished or even completely abolished. For example, the binding affinity of the modified antibody described in Queen et al., supra, is reported to be reduced three-fold; in Co et al., supra, is reported to be reduced two-fold; and in Jones et al., supra, is reported to be reduced two- to three-fold. Other reports describe order-of-magnitude reductions in binding affinity. See, e.g., Tempest et al., Bio/Technology, 9:266-271 (1991); Verhoeyen et al., Science, 239:1534-1536 (1988).
Examples of therapeutic targets for antibody therapy in humans are T lymphocytes, or T cells. Various T cell-reactive antibodies have been described, primarily from murine hybridomas. The specific subsets of T cells recognized by these antibodies, and their cell surface targets, are differentiated by the Clusters of Differentiation System (hereinafter referred to as the "CD System"). The CD System represents standard nomenclature for molecular markers of leukocyte cell differentiation molecules. See Leukocyte Typing III White Cell Differentiation Antigens (Michael, ed. Oxford Press 1987), which is incorporated by reference herein.
So-called "pan T cell" markers (or antigens) are those markers which occur on T cells generally and are not specific to any particular T cell subset(s). Pan T cell markers include CD2, CD3, CD5, CD6, and CD7.
The CD5 cluster antigen, for example, is one of the pan T cell markers present on about 85-100% of the human mature T lymphocytes and a majority of human thymocytes. The CD5 marker is also present on a subset, about 20%, of B cells. Extensive studies using flow cytometry, immunoperoxidase staining, and red cell lysis have demonstrated that CD5 is not normally present on hematopoietic progenitor cells or on any other normal adult or fetal human tissue with the exception of the aforementioned subpopulation of B cells.
Further information regarding the CD5 marker is found in McMichael and Gotch, in Leukocyte Typing III White Cell Differentiation Antigens (Michael, ed. Oxford Press 1987). The CD5 molecule has also been described in the literature as reactive with immunoglobulins. See, e.g., Kernan et al., J. Immunol., 33:137-146 (1984), which is incorporated by reference herein.
There are reports of attempted treatment of rheumatoid arthritis patients with monoclonal antibodies against CD4. See Horneff, et al. Arthritis and Rheumatism 34:2, 129-140 (February 1991); Goldberg, et al., Arthritis and Rheumatism, Abstract D115, 33:S153 (September 1990); Goldberg, Journal of Autoimmunity, 4:617-630 (1991); Choy, et al. Scand. J. Immunol. 36:291-298 (1992).
There are reports of attempted treatment of autoimmune disease, particularly rheumatoid arthritis, with an anti-CD7 monoclonal antibody. See Kirkham, et al., British Journal of Rheumatology 30:459-463 (1991); Kirkham, et al., British Journal of Rheumatology 30:88 (1991); Kirkham, et al., Journal of Rheumatology 19:1348-1352 (1992). Lazarovits, et al., J. Immunology, 150:5163-5174 (1993), describe attempted treatment of kidney transplant rejection with a chimeric anti-CD7 antibody. There is also a report of an attempt to treat multiple sclerosis with an anti-T12 antibody and a pan T- cell antibody (anti CD-6). Hafler, et al. , Neurology 36:777-784 (1986).
None of the above attempts for therapy of human autoimmune diseases involve the use of unconjugated anti-CD5 antibodies.
Thus, there exists a need for the successful antibody therapy of T cell-mediated diseases such as autoimmune disease, graft-versus-host disease, and transplant rejection. As demonstrated by the foregoing, there also exists a need in the art for methods for the preparation of humanized antibodies useful in the treatment of various human diseases and not subject to the foregoing drawbacks.